1. Field of the Invention
The present invention relates to a direct liquid feed fuel cell for charging a rechargeable battery.
2. Discussion of the Background
Generally, direct liquid feed fuel cells generate electricity by an electrochemical reaction of an organic compound fuel, such as methanol or ethanol, and an oxidant, i.e. oxygen, and they have very high energy and power density. Since direct liquid feed fuel cells directly use a liquid fuel such as methanol, peripheral devices, such as a fuel reformer, are not required and fuel storage and supply are easy.
As FIG. 1 shows, a direct liquid feed fuel cell may include an electrolyte membrane 1 arranged between an anode 2 and a cathode 3. The anode 2 and the cathode 3 include fuel diffusion layers 22 and 32 for fuel supply and diffusion, catalyst layers 21 and 31 for the redox reaction of fuel, and electrode support layers 23 and 33, respectively. A catalyst for electrode reaction may be a noble metal catalyst, such as platinum, which has good catalytic characteristics even at low temperature. A transition metal-alloy catalyst derived from ruthenium, rhodium, osmium, nickel, etc., may be used to prevent catalyst poisoning by reaction byproducts (i.e. carbon monoxide). The electrode support layers 23 and 33 may be carbon paper, carbon cloth, etc., and they may be water-proofed to facilitate the fuel supply and the reaction product discharge. The electrolyte membrane 1 may be a 50-200 μm thick polymer membrane. A proton exchange membrane containing moisture and having ionic conductivity may be used as the electrolyte membrane 1.
Among direct liquid feed fuel cells, direct methanol fuel cells (DMFCs) using a mixed fuel of methanol and water involve two electrode reactions: fuel oxidation (anode reaction) and oxygen reduction in the presence of protons (cathode reaction). These reactions may be summarized as follows:Anode reaction: CH3OH+H2O→CO2+6 H++6 e−Cathode reaction: 3/2 O2+6 H++6 e−→3 H2OOverall reaction: CH3OH+3/2O2→2 H2O+CO2 
At the anode 2, where fuel oxidation occurs, methanol reacts with water to produce carbon dioxide, protons, and electrons. The generated protons travel to the cathode 3 through the electrolyte membrane 1. At the cathode 3, where oxygen reduction occurs, protons, electrons, which are supplied from an external circuit, and oxygen react to produce water. Hence, in the overall reaction of DMFCs, water and carbon dioxide are produced through methanol and oxygen reaction. Here, reaction of 1 mole of methanol with oxygen produces 2 moles of water.
U.S. Pat. No. 6,326,097 discloses a fuel cell for charging a cellular phone battery. The fuel cell is useful in charging portable electronic device batteries.